Long-term memory formation consists of multiple phases. A new memory is initially labile. To become stable this new memory undergoes a process known as consolidation that, in the case of declarative memories, occurs within the medial temporal lobes and requires gene expression. When recalled, memories reenter a new phase of vulnerability and seem to require a "reconsolidation" process in order to be maintained. The goal of this project is to characterize, particularly in the temporal lobe regions hippocampus and amygdala, the gene expression regulation underlying different phases of long-term memory formation. It has been shown that members of the transcription factor family cAMP response element binding protein (CREB) play an essential role in the consolidation of long-term memory. However, the cascade of events activated downstream of CREB is still poorly understood. In Inhibitory Avoidance (IA) learning, a significant and persistent activation (phosphorylation) of CREB and CREB-dependent gene expression occur in the hippocampus. We have recently found that a CREB-downstream evolutionarily conserved molecular event essential for IA long-term memory consolidation is the induction of another transcription factor, a member of the CCAAT enhancer binding protein (C/EBPBeta). Preliminary data suggest that, together with C/EBPBeta, another member of the C/EBP family C/EBPdelta, may play a role in memory consolidation. We have also identified a number of putative CREB-C/EBPdownstream genes. Two of these, Insulin-like growth factor-Il (IGF-II) and cyclin-dependent kinase 5 (CDK5), may have a critical role as modulators of the synaptic morphological changes that underlie memory storage. In contrast, the molecular mechanisms of "reconsolidation" are not yet known. In this project we propose to continue our characterization of the gene cascade underlying memory formation, and specifically to: 1- Characterize the anatomical and temporal profiles of CREB-C/EBPBeta activation and asses the contribution of this molecular pathway to the storage of medial temporal lobe-dependent memories; 2- Determine whether C/EBPdelta plays an essential role as a memory activator or repressor. 3- Determine the role of the target genes CDK5 and IGF-II. 4. Characterize the molecular basis of the memory "reconsolidation" process. The proposed experiments will provide significant insight into the molecular mechanisms of memory consolidation. An understanding of the molecular changes underlying memory formation may indicate new strategies for the treatment of memory disorders.